This invention relates to a coffee bean roasting device for roasting coffee beans and the like.
In heating and conditioning coffee beans, good flavor, smell and the like of coffee are generally obtained by rapidly cooling the coffee beans after they have been heated (roasted). In this case, it is the most important factors how to set roasting temperature and time, cooling characteristics after roasting and the like in order to improve quality of the roasted coffee beans.
A coffee bean roasting device has been known having bar-like heaters for heating coffee beans as disclosed in Japanese Utility Model Application Publication No. 63-17,356. Another coffee bean roasting device has also been known wherein coffee beans are offset onto one side in a roasting drum and roasted as disclosed in Japanese Utility Model Application Publication No. 60-41,117.
With these devices of the prior art, however, coffee beans are generally insufficiently agitated in a roasting drum so that they are subjected to less radiation from heaters. In case of the offset coffee beans in the drum, the roasting is so insufficient that it takes undue long time for complete roasting.
In the device of the prior art, moreover, as the heating means are bar-like heaters, it is difficult to heat the coffee beans from their circumference uniformly and without exception. It is furthermore difficult to make the coffee beans be sufficiently subjected to convection heat in the drum.
In order to agitate coffee beans sufficiently in a drum to make the roasting progress uniformly, it has been proposed to provide agitating blades in the from of thin plates on inner circumferential walls of the drum. The coffee beans are roasted by radiation from infrared heaters while being agitated by the blades in this manner.
However, as the blades are generally made of punching plates whose edges 8 have notches 8a, during roasting the notches 8a of the blades bite the coffee beans being agitated by the blades as shown in FIG. 1. Therefore, some coffee beans are split by the notches and the beans held by the notches are over-heated and burnt to cause smoking and firing.
In the devices of the prior art, burnt gases produced in a drum are exhausted out of the device by means of circulation fans or by natural draft through exhaust ports communicating with the inside of the drum.
With the device using the circulation fan, means for regulating rotating speeds of the fan is separately needed so that the device becomes complicated and expensive. In the device using the natural draft, amounts of the exhaust gases cannot be adjusted so that roasted coffee beans include smell of smoke. Moreover, in case that chaffs of coffee beans remain in the drum, such residues frequently make smoky the roasted coffee beans.
In general, moreover, when the negative pressure in the roasting drum is slight, the burnt gases are likely to remain in the roasting drum and peeled chaffs tend to remain in the roasted coffee beans so that the roasted coffee beans often becomes smoky. On the other hands, when the exhaust gases in the drum are intensively exhausted, the negative pressure in the drum becomes higher. As a result, good smell and flavor of the coffee beans are carried away by the exhaust gases forced out of the device.
With an device hitherto used, moreover, when the roasting has been completed, further progress of roasting is arrested only by shutting off the heat sources as disclosed in Japanese Patent Application Laid-open Nos. 56-72,678 and 56-72,679. In other device, a roasting section is tilted by a tilting mechanism so as to exhaust the roasted coffee beans into an external cooling section to promote the cooling of the roasted coffee beans as disclosed in Japanese Patent Laid-open No. 61-199,777.
With such a hitherto used device whose heat sources are adapted to be shut off when the roasting is finished, there is a risk of roasting unduly progressing due to thermal inertia in an oven after the roasting has been completed. In the device whose roasting section is adapted to be tilted, there are irregularities in progress of the roasting and a driving mechanism is needed to tilt the roasting section to make the device complicated.